Pyrolysis employs high temperatures in a relatively oxygen free environment to remove volatiles, as well as gases that can be released at high temperature from breaking down a feedstock. Depending on the feedstock, the volatiles can then be burned to produce usable energy.
It is known to pyrolyze trash, old tires, and other municipal wastes. A typical waste treatment system utilizing pyrolysis includes an input structure for introducing the waste; a chamber or retort from which air can be restricted, and some sort of conveyor mechanism for moving the waste through the system. A dual housing is commonly used, in which the conveyor mechanism conveys the waste through the inner housing, heated gas (exhaust) is introduced into the space between the housings, and heat is conducted to the waste through the walls of the inner housing.
U.S. Pat. No. 5,178,077 to Norris et al. (January 1993) teaches use of dual parallel screws for removing volatiles from soil. Norris, however, contemplates temperatures of only 800° C., and therefore fails to teach the use of dual conveyors in the context of pyrolysis. Indeed, the temperatures of Norris are sufficiently low that there is no need for inner and outer housings, and apparatus or methods for efficiently transferring heat into an inner housing.
U.S. Pat. No. 6,758,150 to Ballantine et al. (July 2004) teaches use of dual screws to transport waste in a pyrolyzer operation, but the screws are not operated in parallel. One of the screws is outside the pyrolyzer. U.S. Pat. No. 4,759,300 to Hansen et al. (July 1988) teaches a dual screw for conveying waste. In that case, both screw conveyors are disposed within the pyrolyzer, but the screws are still not operated in parallel. The output of one screw conveyor provides partially pyrolyzed material input to the other screw. U.S. Pat. No. 7,182,028 to White (February 2007) also teaches dual conveyers (although not a screw conveyor) disposed within a pyrolyzer, but there again the output of one conveyor provides partially pyrolyzed material input to the other conveyor.
Norris, Ballantine, Hansen, White, and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply
Thus, there is still a need for a pyrolyzer with dual processing shafts, and for more efficient transfer of heat through the wall of the inner housing.